Originally Posted by G8rs Fan
Thanks for the information. Any suggestions of pre-fab ones that are available online?
Choose your sub first based upon the power you want and the amount of money you want to spend. That will drive the size of your enclosure; in order to operate properly, different size subs need different size enclosures.
Here's a useful article on the topic:
How To - Car Stereo - Building a High-End Enclosure For a High-End Subwoofer System
Alternatively, decide how much space you're willing to give over to the enclosure and then buy the according size of subwoofer. Bear in mind that it doesn't have to be a square box, as long as you have the right volume you can play with the shape of the unit (within reason).